Touchscreen displays are able to detect a touch such as by a finger or stylus within an active or display area. Use of a touchscreen as part of a display enables a user to interact with an electronic application by touching the touchscreen. The display may present images to the user. Such images may include user interface constructs such as different buttons, images, or other regions that can be selected, manipulated, or actuated by touch. Touchscreens can therefore provide an effective user interface for cell phones, GPS devices, personal digital assistants (PDAs), computers, ATM machines, and other such devices.
In capacitive sensor based, a touch changes a capacitance at a node in an array of electrodes overlaying the display device. There are several different types of capacitive touchscreens, such as mutual and self capacitance types. Self capacitance type touchscreens measure the change of capacitance on a row or column. Mutual capacitance type touchscreens measure the change of capacitance on a node.
Capacitive touchscreens often use two separate layers of transverse electrodes separated by a dielectric. The intersections of the transverse electrodes form the nodes, and are individually accessed to determine the location of one or more touches. Transparent electrodes such as indium tin oxide (ITO) or transparent conductive polymers may be used to form the array of nodes. Other layouts of electrodes may utilize non-overlapping patterns of electrodes, such as triangle and bar patterns and diamond patterns to minimize interference from an underlying liquid crystal display (LCD). Some touchscreens utilize a single layer layout.
In some two layer touchscreen designs, touches are detected utilizing a quantum charge acquisition method. Drive electrodes may be driven with pulses of electricity, and sense electrodes collect charge transferred from the drive electrode. The amount of charge transferred per pulse varies as a function of where the screen is touched, allowing detection of the location of the touch.